Wireless communication technologies are widely used in nowadays. FIG. 1A illustrates the schematic view of a conventional wireless communication system 1, which comprises a user equipment 11, a relay station 13, a base station 15, and a serving gateway 17. The user equipment 11 is wirelessly connected to the relay station 13, the relay station 13 is wirelessly connected to the base station 15, and the base station 15 is wiredly connected to the serving gateway 17. The relay station 13 extends the serving coverage of the serving gateway 17 so that a user equipment that is not in the coverage of the base station 15 but in the coverage of the relay station 13, such as the user equipment 11, can access the services provided by the serving gateway 17.
Although the introduction of the relay station 13 extends the serving coverage of the serving gateway 17, the radio link between the relay station 13 and the base station 15 is burdened with extra headers. FIG. 1B illustrates a packet 102 that the relay station 13 receives from the user equipment 11, while FIG. 1C illustrates a packet 104 that the relay station 13 transmitted to the base station 15. The packet 104 comprises a relay station header and the packet 102. Since radio resource is scare, the relay station header of the packet 104 burdens the radio link between the relay station 13 and the base station 15.
The burden of a header added by the relay station 13 becomes heavy when a packet being transmitted is a Voice over Internet Protocol (VoIP) packet. FIG. 1D illustrates a schematic view of a VoIP packet 106 transmitted by the relay station 13. The VoIP packet 106 comprises an outer header set 106a, an inner header set 106b, and a payload of voice data 106c. The relay station 13 adds the outer header set 106a to the inner header set 106 and the payload of voice data received from the user equipment 11. The payload of voice data 106c is only 30 bytes. The inner header set 106b is 40 bytes or 60 bytes, wherein the Internet Protocol (IP) header contributes 20 bytes (IPv4) or 40 bytes (IPv6), the User Datagram Protocol (UDP) header contributes 8 bytes, and the Real Time Protocol (RTP) header contributes to 12 bytes. The outer header set 106a is 36 bytes or 56 bytes, wherein the Internet Protocol (IP) header contributes 20 bytes (IPv4) or 40 bytes (IPv6), the UDP header contributes 8 bytes, and the GPRS Tunneling Protocol (GTP) header contributes to 8 bytes. Obviously, both the outer header set 106a and inner header set 106b occupy great percentages in the VoIP packet 106.
A Robust Header Compression (RoHC) method is commonly used to compress a header or a header set of a packet in order to ease the burden on a radio link. The RoHC method cooperates with a profile defining which kind of header should be compressed by which method. FIG. 1E illustrates a compressed packet 110 compressed by an RoHC method on the VoIP packet 106. The compressed packet 110 comprises a compressed outer header set 108, the inner header set 106b, and payload of voice data 106c, wherein the compressed outer header set 108 comprises an RoHC header 108a, a compressed header 108b related to the IP header and the UDP header of the outer header set 106a, and the GTP-U header of the outer header set 106a. After compression, the compressed outer header set 108 has 13 bytes (the RoHC header 108a has 3 bytes, the compressed header 108b has 2 bytes, and the GTP-U header has 8 bytes). It is noted that the compression ratio is not good enough. In addition, current RoHC method can only compress one set of headers, so the inner header set cannot be compressed to further reduce the length of the headers.
The RoHC method can be modified to compress both the outer header set and the inner header set. To achieve that, a new profile has to be designed so that all types of headers in the outer header set and inner header set are included. FIG. 1F illustrates a compressed packet 114 compressed by a modified RoHC method on the VoIP packet 106. The compressed packet 114 comprises a compressed header set 112 and the payload of voice data 106c. The compressed header set 112 comprises an RoHC header 112a, a compressed outer header 112b, and a compressed inner header 112c. After compression, RoHC header 112a has 3 bytes, the compressed outer header 112b has 4 bytes, and the compressed inner header has 2 bytes. Although the size of the compressed header 112 is reduced to 9 bytes, an extra overhead of designing a new profile is required.
According to the above descriptions, a header compression method, a corresponding header decompression method and wireless communication apparatus using them are needed.